1. Field of the Invention
This disclosure relates to an apparatus and process for on-demand attachment or disengagement of components for use as a means in an easy and quiet or nearly silent container closure mechanism or fastener system. As used in this specification quiet and nearly silent can be used interchangeable and mean a sound that is typically less than 60 decibels. Specifically this application deals with the use of elastomers, shape memory polymers, shape memory polymer composites, or elastomeric composites as the connection devices in a fastener system. More specifically this application deals with the use of elastomers, shape memory polymers, shape memory polymer composites, or elastomeric composites as the connection portions in a fastener system which can be used to attach a first part to a second part or act as the closure mechanism for a pocket, box, or other container.
2. Description of Related Art
Shape memory polymers (SMPs) and shape memory alloys (SMAs) were first developed about twenty years ago and have been the subject of commercial development in the last ten years. SMPs are polymers that derive their name from their inherent ability to return to their original “memorized” shape after undergoing a shape deformation. All SMPs have at least one transition temperature (hereinafter “Tg”) at which point the SMP transitions between a hard rigid plastic to a soft, pliable, elastomeric polymer. When the SMP is above its Tg it is soft and elastic, when below its Tg it is rigid. Once the temperature of the SMP is above its Tg the SMP can generally be deformed into the desired shape. The SMP must then be cooled below its Tg while maintaining the desired deformed shape to “lock” in the deformation. Once the deformation is locked in, the polymer network cannot return to its “memorized,” or original shape due to thermal barriers. The SMP will hold its deformed shape indefinitely until it is again heated above its Tg, when the SMP stored mechanical strain is released and the SMP returns to its “memorized” shape. It is important to note that the Tg represents the average temperature at which a material transitions from a rigid polymer to an elastomeric polymer. Because it is an average temperature the polymer can sometimes exhibit limited shape memory recovery below the Tg. Typically this limited recovery is small enough and occurs close enough to the Tg that it does not affect the function for which the SMP is designed.
Shape memory materials derive their name from their inherent ability to return to their original “memorized” shape after undergoing a shape deformation. There are three types of SMPs: (1) partially cured polymers, (2) thermoplastic polymers; and (3) fully cured thermoset polymers. There are limitations and drawbacks to the first two types of SMPs.
Partially cured polymers continue to cure during operation and change properties with every cycle. Thermoplastic polymers “creep,” which mean they gradually “forget” their memory shape over time because they are liquids that become solid upon curing. But unlike thermoset resins, thermoplastic polymers can be softened by application of heat or other stimuli and they can be heated and reshaped repeatedly. Additionally, conventional thermoset resins (those that are not SMP) are liquids that react with a catalyst to form a solid, but they cannot be returned to their liquid state and, therefore, cannot be reshaped without destroying the polymer networks.
The current application uses shape memory polymers which are a set of unique polymers that can be reshaped and formed to a great extent because of their shape memory nature but will not return to a liquid upon application of heat. SMPs utilize the beneficial properties of both thermoset and thermoplastic resins while eliminating or reducing the unwanted properties.
When heated above the transition temperature, the links between the SMP molecular connections are easily contorted, stretched, or reoriented due to their elastic nature. When cooled below the transition temperature, these SMP connections retain their new reoriented shape. In the cooled state SMP behaves as a conventional rigid polymer that was manufactured in that reoriented shape. When heated again, the SMP returns to the elastic state and can be reformed to another reoriented shape, or, if no constraint or outside force is exerted on the SMP, it will return to its original memory shape.
SMPs used in the presently disclosed device are unique thermoset polymers, which, unlike conventional thermoset polymers, can be reshaped and reformed repeatedly because of their dynamic modulus. These polymers combine the most useful properties of thermoplastic polymers with those of a thermoset polymer enabling designers to utilize the beneficial properties of both thermoset and thermoplastic resins while eliminating or reducing the unwanted properties. Such polymers are described in U.S. Pat. No. 6,759,481 issued to Tong, on Jul. 6, 2004 with other thermoset resins seen in PCT Application No. PCT/US2006/062179, filed by Tong, et al on Dec. 15, 2006; and PCT Application No. PCT/US2005/015685 filed by Tong et al, on May 5, 2005 all of which are hereby incorporated by reference.
The term “composite” is commonly used in industry to identify components produced by impregnating a fibrous material with a thermoplastic or thermosetting resin. Generally, polymers and polymer composites have the advantages of weight saving, high specific mechanical properties, and good corrosion resistance which make them indispensable materials in all areas of manufacturing. The use of other fabrics or reinforcements such as carbon nano-fibers, high strain fabrics (meaning a fabric that can be stretched in at least one direction and will return to its original shape), chopped fiber, random fiber mat, fabric of any material, continuous fiber, fiberglass, filamentous material (meaning a material made of filaments) or other type of textile fabric can be used to replace carbon fiber in the above examples. Common structural fastening technologies include mechanical fastening, e.g., bolts, latches, clasps, and adhesives. These approaches are widely-used and provide adequate fastening capability for many long-term applications.
Hook and loop type separable fasteners are well known and are used to join two members detachably to each other. Hook and loop fasteners provide rapid-release, but require a higher force to release per area of material than other fastener systems. This development is more commonly referred to as VELCRO®. Used in nature for thousands of years, the system was discovered in 1951 and was issued as a U.S. Patent in 1955, U.S. Pat. No. 2,717,437, to G. DeMestral. The essential technology behind quick release fasteners has not changed much since the discovery of VELCRO®. While there have been some developments to make a better releasing systems such as use of less force per area of material or using standard latches that are computer controlled, other developments have been limited to using explosives to quickly release dangerous cargoes and unwanted parts, i.e. explosive bolts, etc. Unfortunately, a means for cheap, repeatable attachment and release of large-area flat panels with a nearly silent release has eluded researchers.
These types of fasteners generally have two components disposed on opposing member surfaces. One component typically includes a plurality of resilient hooks while the other component typically includes a plurality of loops. When the two components are pressed together they interlock to form a releasable engagement. The resulting joint created by the engagement is relatively resistant to shear and pull forces and weak in peel strength forces. As such, peeling one component from the other component can be used to separate the components with a relatively small applied force. As used herein, the term “shear” refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to slide relative to each other in a direction parallel to their plane of contact. The term “pull force” refers to an action or stress resulting from applied forces that causes or tends to cause two contiguous parts of a body to move relative to each other in the direction perpendicular to their plane of contact. Hook and loop type separable fasteners can require different release times to maximize effectiveness for different applications. In some applications, release times are not critical whereas in other applications release times are critical and may be on the order of a few milliseconds.
Examples of hook and loop fastener systems using a type of shape memory material are exemplified by U.S. Pat. No. 7,013,536 issued to Golden et al on Mar. 21, 2006 and U.S. Pat. No. 6,920,675 issued to Browne et al on Jul. 26, 2005. An additional fastener system for use in medical devices is described in U.S. Pat. No. 6,086,599 issued to Lee and Fitch on Jul. 11, 2000. Fitch describes a fastener system for use in implanting medical devices in the human body principally. The fastener system described by Fitch, however, is not useful for a system beyond the micro scale described in the patent. The mating geometries described in Fitch and the tool necessary to move the device around in the body would be impractical on a larger scale.
The system described in Golden relies principally on the ability of the hook and loop material to melt, flow and soften upon heating, thus disengaging the fastener system. The system described by Golden, however, cannot be reused without substantial time and effort or a complete replacement of the hook portions.
Browne describes a similar system to that of Golden however. The system described by Browne, as well as Golden, focuses on the disengagement of the fastener system and not on a method to engage the fastener system. Additionally both Browne and Golden limit the scope of the system described to a hook and loop system.
However, there is a need for a high strength, reusable, quick-release fastener system that has not yet been met. These next-generation fastening systems require equal structural integrity and fastening capability, but additionally require the system to be able to exhibit a removal and replacement capability that does not damage the substrate material. Additionally, these next-generation fastening systems require a low force to remove and replace, a rapid release/replacement cycle time, and they must be able to attach to any material, including metals, polymers and composites.
Therefore there is a need in the art for a quick release fastener system that can use different mating geometries with high strength other than a hook and loop. Additionally there is a need for a fastener system that can be reused and easily engaged or disengaged at desired times and with little difficulty and with little or no noise.